The disclosure of Japanese Patent Application No. 2002-126959 filed on Apr. 26, 2002, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The invention relates to a method of calculating engine torque by calculating basic engine torque based on an engine rotational speed and a fuel injection amount, and correcting the basic engine torque.
2. Description of the Related Art
Known technologies that involve control of torque in vehicles may include, for example, transmission control, ABS (Antilock Brake System) control, and traction control. In these technologies, with regard to an engine, actual torque of the engine (engine torque) is controlled to be equal to target torque. Also, with regard to the aforementioned transmission control and the like, a controlled variable of an actuator is calculated according to the actual torque of the engine, and the driving of the actuator is controlled according to the controlled variable. For example, in the case of the transmission control, a controlled variable of a solenoid valve for shifting is calculated according to the actual torque of the engine, and the solenoid valve is driven according to the controlled variable. By driving the solenoid valve in this manner, a hydraulic circuit is switched and a certain gear position (a first speed, a second speed, a third speed, or the like) is determined, so that shifting is performed. Also, in the case of the ABS control, a controlled variable of a brake hydraulic pressure of a wheel cylinder is calculated according to the actual torque of the engine, and the actuator is driven according to the controlled variable. By driving the actuator in this manner, the brake hydraulic pressure is controlled, and a slip ratio between the wheel and a road surface is maintained at a desirable value. Accordingly, in order to perform the transmission control and the like, it is required to calculate the actual torque of the engine accurately in the torque control of the engine.
In this regard, for example, in Japanese Patent Laid-Open Publication 200-0127807, the engine torque is calculated as follows. First, basic engine torque is determined based on an engine rotational speed and a fuel injection amount. In addition, a correction coefficient is determined based on a parameter, such as an intake air amount and an intake air pressure, which is considered to have an influence on the engine torque. Then, the engine torque is calculated by correcting the basic engine torque using the correction coefficient.
Meanwhile, the degree of the influence of the parameter on the engine torque changes according to an operating state of the engine at this time, such as the. engine rotational speed and the fuel injection amount. In this regard, in the technology disclosed in the aforementioned patent publication, only a single correction coefficient is set for each type of a parameter, and no consideration is given to the fact that the degree of the influence as described above changes. Thus, if the degree of the influence of the parameter on the engine torque varies according to the operating state of the engine, the varying degree of the influence cannot be reflected in the calculation of the engine torque. Therefore, in the method disclosed in the aforementioned patent publication, there is a limit to improving the accuracy of calculating the engine torque.
It is an object of the invention to provide a calculation method by which engine torque can be calculated with higher accuracy than when basic engine torque is corrected simply by a certain parameter.
A first aspect of the invention relates to a method of calculating engine torque by calculating basic engine torque based on an engine rotational speed and a fuel injection amount, and correcting the basic engine torque using a predetermined parameter which has an influence on the engine torque. In this calculation method, a torque sensitivity coefficient corresponding to an amount of change in the engine torque when the parameter changes by a unit amount is calculated based on at least the engine rotational speed, and the basic engine torque is corrected using the calculated torque sensitivity coefficient.
According to the aforementioned calculation method, the basic engine torque is calculated based on the engine rotational speed and the fuel injection amount. This basic engine torque is the. torque when the engine is in a standard state. Also, the torque sensitivity coefficient associated with the predetermined parameter is calculated based on at least the engine rotational speed. The parameter has an influence on the engine torque, and the torque sensitivity coefficient corresponds to the amount of change in the engine torque when the parameter changes by a unit amount.
Then, the basic engine torque is corrected using the parameter and the torque sensitivity coefficient. As described above, the torque sensitivity coefficient is calculated based on the operating state of the engine (at least the engine rotational speed) at this time. That is, the calculated torque sensitivity coefficient corresponds to the operating state of the engine. Thus, it is possible to determine the engine torque on which the parameter has an influence whose degree corresponds to the current operating state of the engine, by correcting the basic engine torque using the parameter and the torque sensitivity coefficient.
Accordingly, even if the degree of the influence of the parameter on the engine torque changes according to the operating state of the engine such as the engine rotational speed, the engine torque that reflects the changed degree of the influence is calculated. As a result, it is possible to improve the accuracy of calculating the engine torque as compared with the case where the basic engine torque is corrected using a single correction coefficient that is set depending upon the type of the parameter.